Suction
Valve Unloaders
See Cylinder
Action, Single Acting for a drawing of a suction valve unloader installed
on a cylinder.
A valve plate depressor type suction
valve unloader will depress the suction valve plate against the valve
guard to hold the valve open, therefore deactivating the end of the cylinder
by allowing gas to pass through the valve during both intake and compression
stroke. A valve plate depressor type suction valve unloader is actuated
using air or natural gas as actuation gas (usually 70 to 100 psig). In
most cases, the suction valve unloaders are normally loaded, with air
or gas actuation pressure required to unload the cylinder end. Suction
valve unloaders may be used only on plate or ring valves (not poppets).
Applications that require suction
valve unloaders must be reviewed by Ariel / Hoerbiger before quoting.
The valve depressors are always in the seat flow passages. This will reduce
the valve equivalent area and increase the horsepower losses of the valve.
Temperatures may also be increased due to a recirculation of the gas on
the deactivated end preheating the active end. It is important that data
regarding the entire range of suction pressures and gas compositions be
submitted for review. The review will specify the valve plate materials,
lifts and valve equivalent flow areas to be used for the application.
Suction valve unloaders must be installed on all suction valves of the
end being deactivated.
Ariel recommends using suction
valve unloaders on the head end of cylinders only. Crank end deactivation
may result in a non-rod load reversal situation. All
deactivation configurations should be analyzed at all conditions to verify
adequate rod load reversal.
Single acting cylinder operating
cases should be considered when analyzing torsional
responses and acoustical pulsation responses. Single
Acting cylinders can present the worst case scenario for a torsional analysis
due to a more dynamic torque effort curve and for an acoustical pulsation
analysis due to a change in the number of pulses per cycle. High
torsional vibration and / or high acoustically driven vibration can result
from single acting cylinder operation when not considered in these analyses. High torsional vibrations can
increase coupling and shaft stresses, driver functionality and auxiliary
driven equipment integrity. High
acoustical pulsations can increase frame, cylinder, gas piping and equipment
vibrations.
An alternate method of single
acting a cylinder is by removing the head end suction valves on one cylinder
end. Suction
valve removal will result in less horsepower loss as the unloading flow
area is greater.
Cylinders with suction pressures
above 750 psi and or small valve sizes may not be suitable for suction
valve unloaders.
Ariel
Corporation Application Manual
30 July 2003